chapter 19 origin and history of...

Origin and History of Life

Chapter 19


2

OutlineOrigin of Life

Primitive Earth

Origin of First Cells

History of Life

Fossils

The Precambrian

The Paleozoic

The Mesozoic

The Cenozoic

Factors Affecting Evolution

Continental Drift

Mass Extinctions


4Enlightening Quote

Mark Twain, on science (undoubtedly evolutionary science), wrote:

“There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”


5

Another Enlightening Quote

Francis Crick said out of frustration,

“Every time I write a paper on the origin of life, I swear I will never write another one, because there is too much speculation running after too few facts”

Origin and History of LifeWhat is Life?

organized as cells

respond to stimuli

regulate internal processes (aka homeostasis)

• use energy to grow

- metabolism

develop

reproduce

- heredity

DNA / RNA

- adaptation & evolution


The Origin of Life is Hypothesis

Special Creation

Was life created by a supernatural or divine force?

not testable

Extraterrestrial Origin

Was the original source of organic (carbon) materials comets & meteorites striking early Earth?

testable

Spontaneous Abiotic Origin

Did life evolve spontaneously from inorganic molecules?

testable


8

Origin of

the First

Cell(s)


When did life form?

Age of the Earth: 4.6 billion years

Oldest rocks: 3.8 – 4.0 billion years

Oceans established > 3.8 billion years ago

Life not possible during period of heavy bombardment ~ 4.0 billion years ago

Signatures of life: 12C/13C suggests photosynthetic life existed ~ 4.0 billion years ago


Earliest life on Earth

Stromatolites ~ 3.8 billion years old

Earliest known fossils ~ 3.5 billion

years old


Where did life form?

Rule out lands of the Earth

Oceans, lakes, ponds, tide pools?

Deep ocean geothermal vents?


12

The Primitive EarthPrimitive atmosphere:

Most likely consisted of:

- Water vapor

- Nitrogen

- Carbon dioxide

- Small amounts of hydrogen and carbon monoxide

Little free oxygen (anaerobic respiration)

Originally too hot for liquid water to form

Earth cooled and water vapor condensed to liquid water

Origin and History of LifeStanley Miller

University of Chicago

produced-amino acids

-hydrocarbons-nitrogen bases-other organics

It’s ALIVE!


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Monomers EvolveStanley Miller (1953)

Conducted an experiment

Showed that biochemicals could be produced from simple nonbiological sources

-Primitive atmospheric gases

-Strong energy sources

Led to theory of the Hot Thin Soup


Miller Urey Experiment

Water vapor + methane + H2 + (CH4) + ammonia (NH3)

Primitive ocean

Source of energy

Condensation and recycle

Ran for a week

Condensed mixture contained amino acids and complex organic molecules


Problem – early atmosphere was mostly CO2, little methane and ammonia

Experiment redone with CO2 and UV light

Less quantities but produced all amino acids found in life on Earth

Complex sugars and lipids formed

All 5 chemical bases used in DNA and RNA formed

Miller Urey Experiment

17Miller’s & Urey’sApparatus & Experiment.

Notice no O2


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Monomers EvolveAleksandr Oparin’s 1938 Hypothesis:

Suggested organic molecules could be formed in the presence of outside energy sources:

1) methane (CH4)

2) ammonia (NH3)

3) hydrogen (H2)

4) water (H2O)

Experiments performed by Stanley Miller and others show these gases in the primitive atmosphere reacted with one another to produce small organic molecules


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Monomers EvolveThese complex molecules included:

acetic acid

Formaldehyde

amino acids

These kinds of molecules would later serve as monomers, or building blocks, for the synthesis of polymers.

Lack of oxidation and decay allowed organic molecules to form a thick, warm organic soup


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The Earth & Atmosphere

The primitive atmosphere contained little free oxygen (O2) and was a reducing atmosphere as opposed to the oxidizing atmosphere of today.

A reducing atmosphere lacks free O2and allows formation of complex organic molecules.

An oxidizing atmosphere contains free O2 and inhibits formation of complex organic molecules.


21

Monomers Evolve

A.I Oparian and J.B.S. Haldaneindependently theorized that simple molecules were able to form only because oxygen was absent. As a very reactive molecule, oxygen had it been present, would have prevented the formation of organic molecules by supplanting most reactants in chemical reactions


22

Monomers Evolve

Stanley Miller tested the theories of Oparin and Haldane by simulating an experiment under primordial conditions. He applied electric sparks to simple gases (but no oxygen) connected to a flask of heated water. After one week, the water contained various organic molecules including amino acids.


23Flaws in Miller-Urey Experiment

O2 present in primitive atmosphere

Kenneth Towe (Smithsonian Institute paleobiologist) reviewed the evidence in 1996 & concluded that “Early earth very likely had an atmosphere that contained free oxygen”

British geologists Harry Clemmey and Nick Badham wrote that the evidence showed “from the time of the earliest dated rocks at 3.7 billion years ago, Earth had an oxygenic atmosphere.”



Primitive atmosphere not a reducing atmosphere.

1953 Miller-Urey (reducing atmosphere)

- Methane, ammonia, hydrogen & water

1960’s Heinrich Holland, Princeton University geochemist & Philip Abelson, Carnegie Institute geophysicist – (neutral atmosphere)

- Water vapor, carbon dioxide, nitrogen & hydrogen

Abelson concluded, “What is the evidence for a primitive methane-ammonia atmosphere on Earth? The answer is that there is no evidence for it, but much against it.”



National Geographic March 1998 carries a photo of Stanley Miller next to his experimental apparatus. The caption reads:

“Approximating conditions on the early Earth in a 1952 experiment, Stanley Miller – now at UCSD – produced amino acids. ‘Once you get the equipment together it’s very simple’ he says”

Several pages later the article explains, “Many scientists now suspect that the early atmosphere was different from what Miller first supposed”

BUT A PICTURE IS WORTH 1,000 WORDS!!!


Other sources of Organic Molecules

External sources (comets, asteroids, meteors)

100’s of tons of debris fall to Earth each year

Murchison Meteorite (1969)

74 amino acids – 8 used by life on earth, 55 extraterrestrial found

All 5 bases used in DNA/RNA found

Simple sugars and fatty acids were found


Organic Molecules in Comets


Problems still to overcome

Miller – Urey type experiments do not produce all of the ingredients for DNA and RNA

Earth’s primitive atmosphere still debatable (though the absence of free oxygen is a must!)

Sources of energy are varied

However, definite pathways to life are evident in each experiment

29

Origin of the First

Cell(s)


30

Polymers EvolveMonomers join to form polymers in the presence of enzymes

Protein-First Hypothesis:

-Assumes protein enzymes arose first

-DNA genes came afterwards

RNA-First Hypothesis:

-Suggests only RNA was needed to progress toward formation of the first cell or cells

-DNA genes came afterwards


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The late astronomer Carl Sagan said,

“The receipt of a single message from space’ would be enough to know there’s an intelligence out there. That’s reasoning by analogy – we know that where there’s intelligent communication, there’s an intelligent cause.”

How do we deal with the vast amounts of information stored in the DNA molecule?

Quotes on the Origin of Life


Key Events in Origin of Life

Key events in evolutionary history of life on Earth

life originated 3.5–4.0 bya


Origin of Genetics

RNA is likely first genetic material

multi-functional

codes information

- self-replicating molecule

- makes inheritance possible

- natural selection & evolution

enzyme functions

- ribozymes

- replication

regulatory molecule

transport molecule

- tRNA & mRNA

Dawn of natural selection


Prokaryotes

Prokaryotes dominated life on Earth from 3.5–2.0 bya

3.5 billion year old fossil of bacteria modern bacteria

chains of one-celledcyanobacteria


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Origin of Cells (Protocells)

Protocells:

Hypothesized precursors to the first true cells

A structure with a lipid-protein membrane that carries on energy metabolism

-Semipermeable-type boundary may form around coacervate droplets

-Liposomes form spontaneously in liquid environments


36Heterotrophophic

Prokaryotes formed

If a protocell was a heterotrophic fermenter living on the organic molecules in the organic soup that was its environment; this suggests heterotrophs preceded autotrophs.

A heterotroph is an organism that cannot synthesize organic compounds from inorganic substances and therefore must take in preformed organic compounds. (ex. pathogenic bacteria)

An autotroph is an organism that makes organic molecules from inorganic nutrients.(ex. photosynthetic bacteria)


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A Protocell EvolvesIf the protocell evolved at hydrothermal

vents, it would be chemosynthetic and autotrophs would have preceded heterotrophs.(ex. Chemosynthetic bacteria)

As there was no free O2, it is assumed that protocells carried on a form of fermentation.

First protocells had limited ability to break down organic molecules; it took millions of years for glycolysis to evolve.

38Chemical Evolutionat Hydrothermal Vents

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